Sperg is the local bully at Billy and Mandy's school and their neighborhood. He is often seen tormenting Billy, Irwin, Pud'n (or all three), or other kids to no end. However, Sperg is afraid of Mandy due to her cynical attitude.
In "The Most Greatest Love Story Told Ever," Sperg melts when punch (the drink) is thrown right at him in the fight. In "Battle of the Bands," Sperg was the frontman (lead vocals / lead guitar) until Grim proved that he can join the band and Sperg changed to rhythm guitar while Grim took his place. His head blew up in "Billy and Mandy Moon the Moon" when he sacrificed himself to save the gang but it's pretty unknown why he returned again in Underfist: Halloween Bash where Mr. Bun Bun sent his candy army to destroy Endsville and one of his allies gave Sperg a wedgie.
Sperg is overweight, wears a black tank top, blue jeans, white shoes, and a red hat. In the Battle of the Bands episode, he wore a hat with a spike, and had reddish hair, like Billy's. He has a heart-shaped tattoo that reads: "MOM" on his arm, and he's usually seen wearing a red beanie with a red puffball on top.
Sperg is an 10-year-old boy whose preferred method of terrorizing nerds is by administering his "lethal" wedgies.
Sperg is extremely defensive of his mother. Even though he has brutal strength and force, Sperg is scared of Mandy because she's stronger than him. Sperg's life-long dream when he gets older is to become a dancer and singer on Broadway.
Deep down though, Sperg is lonely and all he really wants is a friend to love and care for him. Sperg tends to be very emotionally sensitive, though he tends to keep this side of him under wraps.
- Despite his brutish nature, Sperg did have some decent character development when he confessed his insecurities to Billy in "Cartoon Network Invaded.”
- In the episode "Puddle Jumping" it shows that Sperg is Billy's next-door neighbor, which isn’t the case for other episodes.
- “Sperg” is also a derogatory slang/word for a person with Asperger's Syndrome.
- According to Maxwell Atoms, despite the misconception that people assumed that's where Sperg's name is based on, Sperg was actually named after a friend of one of the writers from the show's first season, whose last name was Spergel.
- When Sperg is angry when people make jokes about his mom, it is a later similar reference to "Regular Show" where Muscle Man lost his temper with Mordecai and Rigby for making terrible jokes about his mom which leaded him to stop the car and called out his brother to deal with them in the episode "My Mom".
- Also when Sperg is scared of Mandy, it could be a similar reference to Doraemon where Gian is scared of his own mother because she is stronger than him.
- Both he and Grim are voiced by Greg Eagles.